For environmental campaigners who are also republicans, the Prince of Wales is a bit of a thorn in the flesh. He's involved in just about all the principal issues - championing organic agriculture, supporting local produce, rainforest campaigning, and sounding off about GM foods. Whereas in the past it might have been possible to ignore him as an eccentric fellow traveller, these days his views often sound so like those of the leading environmental NGOs, that increasingly they are having to ask themselves: does he know what he's talking about? Is he an asset or a liability?

This questioning is likely to become more insistent over the coming year. Prince Charles turns 60 in November and some people will ask more loudly than before: what is an ageing prince for? Insofar as he asks himself the same question, it seems that focussing on the environment is the answer. Last year he set up Rainforests Project, giving himself a year to come up with action to save the rainforests. The man, whose main role was ticking off politicians and newspaper editors in letters written in green ink, seems to be finally settling on a role as the environmental conscience of the nation.

It is easy to mock Prince Charles - and large sections of the media have done so in the wake of his latest outburst, earlier this week, on GM food. He has a strange, strangulated, plummy accent. He tends towards hyperbole, on this occasion describing GM crops as "the biggest disaster, environmentally, of all time". He often looks and sounds silly, as when he sung the praises of "wibbly wobbly carrots", while dressed in ancient tweeds and carrying a shepherd's crook. And he famously loses his temper, becoming more and more like his irascible father with every passing year. According to Jeff Randall, the Daily Telegraph journalist who interviewed him on this occasion, Prince Charles "jabbed" at him with his finger and was "bouncing in his chair" while setting out "his nightmare vision", a world in which millions of small farmers "are driven off their land [by global conglomerates] into unsustainable, unmanageable, degraded and dysfunctional conurbations of unmentionable awfulness". Out of context, that statement rivals his views on nanotechnology a few years ago - comments which came to be known as his "grey goo" moment after he apparently spoke of the horror of such technology turning the world to grey goo.

But even though many newspapers wheeled out scientists to denounce Prince Charles as "unscientific", he has garnered significant support. Several commentators noted that in fact the scientific community was far from united in support of GM crops, while Patrick Holden, the director of the Soil Association, rallied to support his seriousness and expertise. The Daily Mail, consistent in its hostility to GM "Frankenstein foods", said Prince Charles had "put forward serious arguments that need to be heard and struck a resounding chord with the public".

"His comments are being misrepresented," says journalist Felicity Lawrence. "He was actually talking at the time about how to support local food producers in Scotland, something he knows a lot about. I suspect his explosion about farmers going to live in horrible cities wasn't like his denunciation of the modern UK city along the lines of his 'hideous carbuncle' speech, it was addressing how, if you pursue further industrialisation of agriculture, it inevitably means growers are displaced from the land and will end up in mega slums. This isn't wild fantasy. It's describing what is happening."

No one doubts Prince Charles's commitment to the environment. It has been a lifelong passion - sometimes derided, as when he famously announced that he always talked to his plants, but often prescient. He set up a natural filter bed and water recycling system at Highgrove in Gloucestershire long before most people were aware of the need to conserve water. His Rainforests Project makes explicit his desire to make an impact in his 60th year on what he considers the world's most pressing problem: deforestation. But the cause to which he remains closest is promoting organic food production and small-scale local farming. He's been an organic farmer since the 1980's, and set up the highly profitable Duchy Originals in 1992. An organic food company, it helps small farmers find new markets for their goods while promoting more sustainable production.

"He has many interests," says Paddy Harverson, his communications secretary. "But farming is right at the top not least because he's a farmer. He spends a lot of time on Home Farm in Gloucestershire and takes an immense interest in contemporary farming. This year he is Patron of the Year of Food and Farming and most small farmers would see him as a friend and advocate.

"The Daily Telegraph interview was given to highlight The North Highland Initiative. That's one of the four or five initiatives he has set up to help farmers' products become more competitive by using imaginative marketing solutions."

The prince's interest in food and food production is one of the main reasons he is once again mired in political controversy. The current food crisis, say critics of the food industry, has allowed the supporters of GM to come rushing back into government circles offering biotechnology as a solution. His spokespeople are keen to insist that debating issues of food production and food security are not political but social and environmental. But as the global food crisis moves centre stage and politicians position themselves, that distinction will be harder to maintain. Could Prince Charles become more than a royal mascot for the greens? His seriousness is not in dispute but does he have the depth of understanding to be a spokesman environmentalists would be happy to line up behind?

"Was he talking nonsense?" says Andrew Simms, the policy director at the New Economics Foundation. "No, but I think he was overstating it. If someone asked me what was the most serious issue affecting the environment at the moment I'd say climate change rather than biotechnology. Biotechnology is a very important issue. There are lots of scientific and health issues connected with it that are still unanswered. But the most important issue about biotechnology is that the vast majority of applications which have come out of research into GM have had nothing to solving the problems of poverty, hunger and food security and everything to do with extending the control which agri-business has over the food chain."

According to Simms, tackling food security and hunger necessarily entail issues of social justice and redistribution. "If you do ask how to go about solving those issues, biotechnology would be quite low down. Higher up would be solutions such as giving people more entitlement to the land, land reform, redirecting agricultural extension services to small farmers, and looking at a wide range of sustainable farming techniques which don't rely on invasive high technology approaches but build on farmers' existing knowledge."

And if the real solutions to food security and sustainable food production entail equitable redistribution, where does Prince Charles - a person of immense, almost unimaginable privilege, stand on these issues? "What is really interesting" says Lawrence, "is that he's talking about corporate control and its effect on agriculture. It's not exactly leftwing but it is radical. I would place him in that tradition of philanthropic, experimental landowners like Robert Owen, who does things in a patriarchal and paternalistic way but genuinely wants to leave the world a better place."

There are other examples of this kind of paternalistic philanthropy in Britain, including around food production. Mac Fisheries was set up by William Hesketh Lever, one of the Lever Brothers, in the early 1920s as an attempt to guarantee work for the fishing community on and around the Isle of Harris.

It may also be the case that environmental issues are recasting the old left/right divisions. Figures such as Zac Goldsmith, Peter Melchett, Jonathan Porritt and even David Cameron - people who might all fit the description "radical toffs" - are involved in causes which could easily bring them into conflict with the activities of big corporations. But even if old alignments are changing there is a long way to go to overcome most people's ambivalence about embracing Prince Charles as a green superhero or even as a spokesman.

"He says he's concerned," says Simms. "But he doesn't strike me as being too concerned about poverty and poverty reduction." Others would be harsher. Ken Wharfe, the former royal protection officer for Princess Diana who had the opportunity to observe the prince at first hand, says: "The point is that Charles, for all his current 'voice of the people' role, is someone whose life is wrapped in cotton wool, where every whim is catered for and not challenged.

"I remember leaving Balmoral one evening with the Prince of Wales in a convoy of four vehicles, suddenly to be instructed to return immediately to the castle. Fearing a real emergency I asked why, he told me that he had left an electric light on, and not to turn it off would be a terrible waste of electricity. So the whole convoy returned to extinguish the light. I don't begrudge the Prince of Wales his reed and lily bed for the natural recycling of liquid waste. It's just that no one seems to notice how totally at odds it is with all the devotion to detail and excess which is the hallmark of his life at Highgrove."

"Prince Charles is who he is and says what he says. And that's fine" adds Simms. "But I don't think he should stand as a spokesperson for the broader environmental and social justice system. The trouble is we are trapped in a celebrity culture and royalty is part of that. There are many voices out there possibly more suited to speak - people who know more about the issues in greater depth and from the perspective of global justice. But it's a celebrity system and celebrities crowd out more informed voices."